14 



Conservation Department 



hi*-!! air tem])erature followed by warm nights will send the water 

 iij) a little higher each day. Some judgment has to be exercised 

 in the use of such a table. It has not been possible to extend 

 the range below 80° (for air) because the temperature differences 

 between trout and non-trout streams under such conditions 

 frequently are too small to estimate. 



Brown and rainbow trout w^aters require a different table 

 because these fishes tolerate higher temperatures than brook trout. 

 The following has been used during the present survey. It is 

 based similarlv to the one given above. 



TAni-E 2. 



CoMPAKisox OF AiK Axi) ^YATI<:l{ Tempekati'kes in a Stream 

 Tolerated by Brown ani> Rainbow Tkoit 



Max. air temp. deg. Fahr. . . 

 Max. water temp. deg. Fahr. 



94.0 

 80.0 



It is well at this time to mention three important influences 

 tending to hold down the temperatures of our streams. 



Cold springs: Size, location and frequency of occurrence. — 

 The larger the spring the more slowly the water warms and conse- 

 quently the greater the area available for trout. A stream having 

 springs at the source only usually shows three different regions — - 

 the upper one suitable for brook trout ; the middle, suitable for 

 brown trout, and the lower having only a mixed population of 

 minnows, suckers, etc. 



A stream having springs located at frequent intervals through- 

 out its course also has frequent cold ])ools into which trout may 

 retire on hot days. Practically the entire course of such a stream 

 is available to trout, because on days of average temi)erature the 

 trout may forage in all sections. 



Small unshaded sjirings in exjwsed ]daces away from a stream 

 may have little effect upon the stream because the spring water 

 often warms up to the tem])erature of the stream before it unites 

 with the latter. Such si)rings and consequently the main stream 

 may be improved by shading their courses. 



Stream bed. — Since the tem])erature of the soil just beneath 

 the surface is much lower than that of the air on warm days, the 

 soil tends to absorb heat from the water flowing over it. The 

 effects are much more noticeable in the spring months than in sum- 

 mer, for as the season advances the soil also becomes wai-mer. 

 One may 1lius expect to record highei* water tem])erature in .Iu!y 

 and August than in May and .luiu', for the same air temperatures. 

 Shade: Forest cover. — Trees affect the temperature of a 

 stream in tlie following ways: They keej) cool the stratum of air 

 overlying the water; they |)i-event the stream bed and surrounding 

 ground t'l'oui wai'iiiiiig, holh ol" which have a marked effect u])oii 

 water temixM-nlurc ; and finallx' they eliminate the effect of the 

 direct rays of Ihc snii upon the water. 



Many a good 1i-oul sli-cam has been |)ai'11y oi- wholly spoiled 

 on account of the s1rip|)ing of forest covei-. 



